ABSTRACT
Internal stiffeners are commonly employed to enhance the strength of tubular joints found in offshore steel jacket structures. However, there is a lack of detailed design guidance on the determination of their strengths in major offshore code or design guide. This paper first summarises the results of an extensive finite element study on CHS DT-joints with internal ring stiffeners. The study generated a database of twenty-two stiffened joints, some of which included multiple stiffeners. Observations on the development of plastic zones in the stiffeners show that the failure mechanism is the formation of plastic hinges from bending. A theoretical model based on the observed failure mechanism is then presented. The model is based on upper bound theorem, with a postulated six-hinge collapse mechanism. The proposed theoretical model was found to provide strength predictions to a very high degree of accuracy.
